Human evolution researchers have finally gotten a close look at a set of fossils that have caused one of the biggest sensations in the field of human evolution in years. Last week, the Comptes Rendus de l'Académie des Sciences lifted the embargo on two papers set for publication in its 28 February issue, in which scientists claim that 6-million-year-old bones unearthed in Kenya represent our earliest known ancestor. But experts disagree about the significance of the findings.

The 13 fossil fragments--broken femurs, bits of lower jaw, and several teeth--have been controversial from the start. After they were found in the Tugen Hills of southwestern Kenya last fall by a team led by geologist Martin Pickford of the Collège de France and paleontologist Brigitte Senut of France's National Museum of Natural History, some researchers contended that the fossils had been collected illegally, charges that Pickford and Senut have strongly denied (Science, 15 December 2000, p. 2065[2]; and 9 February, p. 986[3]).

In their papers, the team argues that the bones and teeth belong to a human ancestor and have dubbed it Orrorin tugenensis. If Orrorin is indeed a human ancestor, it would predate other leading candidates by some 2 million years. But Pickford and Senut have a more drastic shake-up in mind for the human family tree. Based mainly on the specimen's teeth, which they say resemble those of modern humans, they believe that all australopithecines--hominids which include the famous skeleton Lucy, whose species is thought to be one of our direct ancestors--should be relegated to a side branch in favor of Orrorin.

Paleoanthropologists are split over the fossils' significance. Milford Wolpoff of the University of Michigan, Ann Arbor, calls Orrorin a "great discovery, one with key information about hominid origins and early evolution." Others aren't so sure. David Begun of the University of Toronto says he can't tell whether Orrorin was "on the line to humans, on the line to chimps, a common ancestor to both, or just an extinct side branch."